Conventionally, a throttle control apparatus in which a motor control unit (valve angle control unit) variably controls an electric power supplied to an electric motor to perform an opening/closing operation of a throttle valve that is rotatably installed in a housing. As an example of the throttle control apparatus, an air intake control apparatus for internal combustion engine is known, in which an electric motor rotationally actuates a valve body of an airflow rate control valve within a predetermined valve angle control range from a full close angle to a full open angle, to variably regulate a quantity of intake air supplied to combustion chambers of the internal combustion engine.
As shown in FIGS. 5-9B, the air intake control apparatus, which actuates the valve body (throttle valve) 101 of the airflow rate control valve to open and close an intake passage, is provided with an actuator that rotationally actuates the throttle valve 101 toward the full open angle and toward the full close angle from a predetermined intermediate angle, and a torsional coil spring 105 that biases the throttle valve 101 from the full open angle or from the full close angle to the intermediate angle. The actuator includes an electric motor 104, a power transmission mechanism that transmits a rotation of a motor shaft 111 of the electric motor 104 to a valve shaft 113 of the throttle valve 101; and a housing 106 that houses the torsional coil spring 105 and the power transmission mechanism therein. The housing 106 is integrally formed with a wall of a cylindrical portion 103 of a throttle body 102 that is opened and closed by the throttle valve 101. The power transmission mechanism includes a pinion gear 107, an intermediate reduction gear 108 and a valve gear 109.
The torsional coil spring 105 includes a return spring 141, which biases the throttle valve 101 from the full open angle to the intermediate angle, and an opener spring 142, which biases the throttle valve 101 from the full close angle to the intermediate angle, to keep the throttle valve 101 in a default intermediate angle at which the throttle valve 101 is slightly opened from the full close angle, to enable a fallback travel (limp home travel) of a vehicle in such a case that an electric power supply to the electric motor 104 is stopped due to any cause.
In this throttle control apparatus, the return spring 141 spirally surrounds a circumference of a cylindrical spring guide 125 of the housing 106 to exert a torsional spring force on the valve gear 109 to rotate the throttle valve 101 from the full open angle to the intermediate angle. The opener spring 142 spirally surrounds a circumference of a cylindrical spring guide 135 of the valve gear 109 to exert a torsional spring force on the valve gear 109 to rotate the throttle valve 101 from the full close angle to the intermediate angle.
In the throttle control apparatus, the return spring 141 and the opener spring 142 can be integrated in one torsional coil spring 105 as shown in FIG. 7, to reduce the number of parts, to simplify a construction, and to decrease a manufacturing cost of the throttle control apparatus. In the torsional coil spring 105, a connection portion of the return spring 141 and the opener spring 142 is bent in a generally U-shape to serve as a U-shaped hook 143. The torsional coil spring 105 is wound in one rotational direction on one side of the U-shaped hook 143, and is wound in the other rotational direction on the other side of the U-shaped hook 143, to provide the return spring 141 and the opener spring 142.
The housing 106 is provided with a first spring end support 151 that supports a first spring end portion (valve-side spring end portion) 144 of the torsional coil spring 105. The valve gear 109 is provided with a second spring end support 152 that supports a second spring end portion (gear-side spring end portion) 145 of the torsional coil spring 105. The U-shaped hook 143 is associated with a C-shaped support 156 of the valve gear 109 to go into an engagement with the C-shaped support 156 and to come out of the engagement.
In the throttle control apparatus disclosed, for example, in JP-2004-301118-A and its counterparts U.S. Pat. Nos. 6,986,336, 7,051,707, EP-1455069-A2, EP-1598538-A2 (which are referred to as Patent document 1 hereafter), the above-mentioned torsional coil spring 105, in which the return spring 141 and the opener spring 142 are integrated, has a coil configuration in which a center axis of the torsional coil spring 105 is previously decentered (offset) in its natural state in a direction opposite to an elastic deformation occurring in a radial direction when the torsional coil spring 105 is installed so that the first spring end portion 144 is supported by the first spring end support 151 of the housing 106 and the second spring end portion 145 is supported by the second spring end support 152 of the valve gear 109. Further, as shown in FIG. 8, both end hooks of the opener spring 142 (i.e., the U-shaped hook 143 and the second spring end portion 145) are aligned with each other in a direction of a torsion axis of the torsional coil spring 105. Thus, a frictional torque caused by a friction between the circumference of the cylindrical spring guide 135 of the valve gear 109 and an inner circumference of the opener spring 142 is reduced when electric power is supplied to the electric motor 104, so as to reduce a reaction torque acting on the electric motor 104.
In FIGS. 7, 9A, 9B, referential numeral 127 designates an intermediate angle stopper that is formed integrally with the housing 106, and reference numeral 129 designates an intermediate stopper member that is screwed in the intermediate angle stopper 127. Further, reference numeral 137 designates a full closure stopper portion that is provided in the valve gear 109, and reference numeral 139 designates a full closure stopper that is formed integrally with the housing 106.
In the valve gear 109 of the throttle control apparatus according to Patent document 1, the second spring end support 152, which supports the second spring end portion 145 of the opener spring 142, is provided separately from the C-shaped support 156, which goes into and comes out of the engagement with the U-shaped hook 143, at which the return spring 141 and the opener spring 142 are connected with each other.
When the throttle valve 101 is actuated to an angle between the full close angle and the intermediate angle as shown in FIG. 9A, the U-shaped hook 143 is moved apart from a support surface of the C-shaped support 156 of the valve gear 109. Thus, the torsional spring force acting on the C-shaped support 156 of the valve gear 109 is zero.
Contrarily, when the throttle valve 101 is actuated to an angle between the full open angle and the intermediate angle as shown in FIG. 9B, torsional spring forces generated by both the return spring 141 and the opener spring 142 are exerted on the support surface of the C-shaped support 156 of the valve gear 109. Thus, the C-shaped support 156 is subjected to a relatively large force. Therefore, it is necessary to form the C-shaped support 156 in a shape having a large thickness, a strengthening rib, etc., to provide the C-shaped support 156 with a rigidity enough to endure the relatively large force.
As described above, the valve gear 109 has the second spring end support 152 and the C-shaped support 156 that are separated from each other, so that the C-shaped support 156 must be provided with a rigidity enough to endure the relatively large force. This configuration of the second spring end support 152 and the C-shaped support 156 upsizes the valve gear 109, and increases manufacturing cost of the valve gear 109.